Re: [gentoo-user] links that behave differently per calling app?

[Grant Taylor]

On 11/10/19 9:37 PM, Caveman Al Toraboran wrote:
> hi - is it possible to have some kind of fancy links that know the
> name of the process that is trying to access it, and based on its name,
> it links it to a file?

I've not heard of that specifically.

> e.g. `ln -s X Y` will create link Y that always refers to X whenever
> anyone tries to access Y.  but is it possible to have a fancier linking
> that creates a linking file that contains some kind of access list,
> that specifies things like:
>
> - if accessing process is named P1, then direct it to X1.
> - if accessing process is named P2, then direct it to X2.
> - ...
> - if accessing process is named Pn, then direct it to Xn.
> - else, default to X0.

However, I have heard of something that might come close to what you 
what I think you're asking about.

I've never heard of support for this in Linux.  But I have heard of an 
ability that /some/ other traditional Unixes have where a named sym-link 
can point to a different file based on the contents of an environment 
variable.

Think of it as something like this:

     ln -s /usr/arch/$ARCH/bin /usr/bin

Thus

     /usr/bin -> /usr/arch/x86/bin   # on x86

-or-

     /usr/bin -> /usr/arch/arm/bin   # on ARM

Depending on what your architecture is and thus the value of the $ARCH 
environment variable.

I /think/ this was done based on environment variables and / or 
something else equally consistent in the kernel.

I have no idea what this type of link is called.  But it is a well 
established standard in the traditional Unix space.  Though, I think 
it's seldom used.

> i think if we have this, we can solve slotting in a simpler way.
> e.g. we install libs in their own non-conflicting locations, and
> then install for them such fancy sym links with access that routes
> accessing processes to the right version of the lib.

Interesting idea.

I'd need to know more about how the links are actually implemented and 
more about slots to even fathom a guess if it would work.  I'm sure it 
would do something.  I just can't say if we would like what it does or not.

I question if environment variables are what's used, mainly because of 
the potential volatility of the environment; different interactive 
shells, different ""shells in /etc/passwd (et al.) that bypass 
interactive shells, remote commands, etc.  I could envision how the 
traditional environment variable might not behave as desired.

I also have concerns about the potential security implications of an end 
user changing something in their interactive shell's environment, thus 
altering where this type of link would point to.

> thoughts?

I would very much like to see this type of functionality come to Linux. 
But I gave up hoping for it a long time ago.



-- 
Grant. . . .
unix || die





-- 
Grant. . . .
unix || die